1. Technical Field
The present invention relates generally to operating a cordless telephone device and specifically to a method of conducting an intercom communication between two cordless telephone handsets in a telephone system incorporating a single base unit and multiple battery powered telephone handsets. While the present invention has utility in any timing critical master--slave system having a master clock generator and associated slave devices synchronizing to the master device, the invention has been disclosed in a cordless telephone embodiment wherein multiple radio transmitter/receivers transmit and receive signals on two or more radio frequencies, such as found in a system implementing a continuous frequency hopping and/or time division duplex protocol.
2. Background Art
Cordless telephones usually consist of one base unit and one handset. The base unit sends voice and data signals to its associated handset and receives voice and data signals from the handset over a radio frequency link. The data signals are utilized by the base unit to manipulate the subscriber telephone line, which is connected to the base unit. For instance, the base unit detects a ring signal on the telephone line and may further place the telephone line in an off-hook state if so directed by the user. The base unit further processes voice signals and transmits and receives both voice and data signals.
Another function typically provided in a prior art cordless telephone is the ability to conduct an intercom conversation between a base unit and remote handset. In an intercom mode a communication link is established between the base unit and the handset in the normal manner. If the base unit initiates the intercom mode the handset typically sounds a tone alerting the user that the base unit is attempting to open a communication channel between the base unit and the handset. The intercom tone typically differs from the tone used to alert the user that the base unit is attempting to open a communication channel to the handset for purposes of processing an outside telephone call. Alternatively, the handset may initiate the intercom mode and signal the base unit accordingly.
Unlike the processing of a conventional telephone call, be it outgoing or incoming, no connection is made to the subscriber telephone line during an intercom call between the handset and base unit.
Prior art cordless telephone devices which contain provisions for conducting intercom communications between a base unit and a handset, particularly a timing critical cordless telephone device which transmits and receives radio signals on two or more radio frequencies implementing a continuous frequency hopping and/or time division duplex protocol, do not include the ability to have two handsets conduct an intercom communication independent of the base unit. Such systems are by design extremely time critical and is wholly dependent upon synchronizing each of the radio transmitter/receiver which make up the system so that communication channels may be opened. One radio transmitter/receiver is typically designated as the master and serves to provide master timing. All other radios in the system, designated slaves, synchronize themselves to the master. Without the ability to synchronize, no radio can communicate with another radio in the system. Thus, omitting the base unit from the communication link would in prior art systems deny the handsets access to the master system timing being maintained by the base unit such that, in a frequency hopping and/or time division duplex system, no two handsets could synchronize or communicate with one another.
Accordingly, it is an object of the present invention to provide a method of conducting an intercom call between two handsets in a cordless telephone wherein multiple radio transmitter/receivers transmit and receive signals on two or more radio frequencies implementing a continuous frequency hopping and/or time division duplex protocol.
It is a further object of the present invention to provide a method for designating a handset as temporary timing master for the duration of an intercom call and relinquishing all master status upon completion of the call.
These and other objects of the present invention will become apparent in light of the present application, specification, claims and drawings.